This invention relates to railroad flat cars and is particularly directed to an articulated, multiple-unit, single-level container flat car. Such cars typically have two end units or platforms supported at their coupler or outer ends on trucks. The end units adjoin one or more intermediate units with adjacent platforms supported on shared trucks. Connections between the units are made at articulated joints.
Container freight represents a significant portion of railroad tonnage. The advent of containerized lading has resulted in complementary advances in the design of railroad rolling stock. Most significant has been the development of so-called double-stack well cars which have the capability of carrying multiple containers, stacked vertically upon one another, two tiers in height.
While such cars are efficient and provide economy of use, double-stack well cars are not suitable for all forms of rail service. Such cars cannot be used in areas where tunnel or other clearances restrict overall height. In such service it is necessary to utilize cars carrying containers at a single level.
Another advance in railroad rolling stock has been the acceptance and use of multi-platform cars which include shared trucks between adjacent platforms connected by articulated connectors. Such cars minimize the car weight-to-lading ratio and maximize load carrying capability. The peculiarities of container configurations create potential problems of excessive rail loading if indiscriminate intermixing of containers is permitted.
Standard containers currently in use have nominal lengths of 20, 40, 45 and 48 feet. The 20 foot container will be called a short container while the others will be referred to collectively as long containers. It is desirable to be able to intermix containers of different sizes on the same car. This can be done by providing appropriately-located retention means.
Intermixing container sizes, however, can lead to overloading the trucks if care is not taken to avoid it. Current standards limit the gross load on rail for a 70 ton truck to 110,000 lbs. including the weight of the truck, carbody and lading. A standard 70 ton truck weighs about 9,000 lbs. Each shared truck carries half the weight of two adjacent platforms, which is about 14,000 lbs. So an empty platform and truck loads the rail to about 23,000 lbs. That leaves 87,000 lbs. for the containers and their lading.
The specified allowable load of the 20 foot container is 52,912 lbs. The specified load limit of the three long containers is 67,200 lbs. Thus, it can be seen that if two long containers are placed adjacent a shared truck, that truck will carry half the weight of the two containers and the rail load limit will not be exceeded. Similarly, if short and long containers are placed adjacent a shared truck, that truck will carry half of the long container load and all of the short container load, and again the rail load limit will be met. However, if two short containers are placed adjacent a shared truck, that truck takes the full weight of both containers which exceeds the rail load limit. The present invention provides a structure that precludes the overload condition just described yet maximizes the utility and efficiency of a multi-platform configuration.